MPPT Vs. PWM Cost Comparison -- Am I doing this right??

[Canine]

I understand what you are saying,but I would like to have some real world unbiased test results.Anyway,people seem to be much calmer on this thread than the gun thread.HA

 

[LeeRevell]

Much less politically charged and biased, even more so on the Global Warming thread. With my basic needs, I expect to start off with a decent PWM. No need for MPPT, at least for awhile.

 

[GotSmart]

At this point in my situation, I am using a PWM.  I only have a single panel, with 448 AH of battery.  I simply do not have the need for a MPPT.  If I got a large power draw item, and another panel I would go with the MPPT.  

As it is with the power use I had when dwelling, I could go two weeks without starting to worry with no power in.  

That is why I always ask how much power will be used before suggesting panels or controller.

 

[MikeRuth]

Looks to me like:If you have room for more panels go with a pwm controller .If space is at a premium,go with mppt.$142 sounds awfully high for a pwm controller.

Not high for one of the best PWM CC. The Tri star TS-45 has some seriously solid specs and capability and reputation.  

I choose that myself as MPPT was just out of my budget for the time being and having just two 100W panels in parallel, PWM was a good choice. 

Mike

 

[GotSmart]

If you have more panels, you need a MPPT. A PWM will only go so high in power handling capability. It is like free power. The PWM handles up to 300W ok, but more than that ~~~Bite the bullet and do it right.

 

[MikeRuth]

GotSmart, please dbl check your information. I'm not sure what CC your referring to. And I'm really not trying to start an argument.

http://www.morningstarcorp.com/wp-content/uploads/2014/02/TriStar-Datasheet-English.pdf

From Tristar, the TS-45 is good to 4KW, Now would I run that much through it? probably not, but my point is when saying something is only good to so much of a spec then you need to offer up the goods on that spec.

 

[jimindenver]

The best I can tell you about researching controllers is to look at user reports. It was a you tube video where the person took apart a Eco-worthy 20 MPPT controller and then ran test that convinced me to take the chance on it. There are a variety of forums for solar, boating, RVing, even here where people discuss the various equipment. They happily boast how wonderful it is or rant on it's failures in their unique situation. It takes time to get a feeling for each controller but the info is out there.

New controllers tend to get shredded on forums by people that have never touched them. Even after you report that they work I hear that it can't be as efficient or it must be the cheap controller if they didn't like the test results. The comparison is hard to come by since most people don't have multiple controllers with matching panel set ups to go with them. For a while I was lucky to have four controllers and seven panels of three different types. I would test different panels on identical controllers, identical panels on different controllers, plus some shade, series, parallel, overcast test, pretty boring stuff. There were a handful of Eco-worthy users chomping at the bit for me to run a side by side with the $500 upgrade and grins all around when the Eco-worthy held its own too. It may not have the bells and whistles but it is just as efficient, producing the same 18.5a from a 250w panel as the Morningstar TS-MPPT-60 did its.

Since efficiency isn't a issue you go looking at reliability, build and features. The Eco-w weakness is features but it is very dependable. Some controllers are very cheaply made or in one video I watched the controller was built like a brick chithouse, too bad it was nuts. Someone writes the programming that controls a MPPT controller, you are buying that too. PWM controllers are controlled by the voltage of the battery, it's much simpler.

The last thing is that over the years I have kept a running tally on who has what, uses it where and gets what out of it. An example is that I'm interested in what Mike gets out of his two 100w panels with PWM because I know of someone using the same with a Eco-w. It's that comparison that I keep in my head. Multiply that not with just the people here but also on two solar forums, four RV forums and the people I know offline and you start getting a general feel for what does what.

So consumer reports may not have done a test yet but the real world info is out there. The easiest route is to buy the expensive OMG it does everything controller and know that all your bases are covered.

 

[jimindenver]

Mike

I don't think gotsmart was saying your controller couldn't handle the power but rather that there is a point in which MPPT is justified. At your level with a few hundred watts there isn't a big enough gain to justify the expense. When you start getting up there in watts the gain builds up to the point that it will make a difference. A amp or two from 200w vs 10 or 15 from a larger array is what he is talking about. 750w in PWM will do a max of 43 amps when the battery voltage is 13.6v. That same 750w in MPPT can come close to maxing out my 60a MPPT controller. I can normally see 55a+ at any voltage tracking the three panels.

For me the difference isn't the peak output but rather the "at any voltage" thing. PWM is at its weakest when I need the power the most, early on when the battery voltage is at its lowest. That's when your 200w on PWM isn't 200w but it is still 200w on MPPT. You wont see the full potential of your panel until the battery reaches 13.6v or what ever voltage the panel is speced at. So in a identical set up a MPPT controller will charge a battery faster. A MPPT controllers weakness is hot panels produce less voltage reducing the advantage it has over PWM.

 

[MikeRuth]

I agree Jim, I'll have to pull couple log files as I haven't been watching my stuff lately. But off the top of my head with my two 100 Watt Kyocera 10 year old panels in parallel, I'm typically seeing 11 to 12 amps when the batteries are in a state to take that much. That has been my peak.
Most of the time my batteries are quite near full and I'm seeing absorption and or float, in that state if I crank up a draw on the system again I'll see a peak of 11 amps typically if I have say the Fan on high 5 amps, the inverter about 5 amps running and charging a laptop and 110 Volt fan running at about 1 to 2 amps.

I do feel that Tristar is a reputable company and builds a quality product.
Being that we are so far from running in the kilowatt ranges I do agree that we need all the efficiency we can get within our budgets. 

Mike

 

[GotSmart]

GotSmart, please dbl check your information. I'm not sure what CC your referring to. And I'm really not trying to start an argument.

http://www.morningstarcorp.com/wp-content/uploads/2014/02/TriStar-Datasheet-English.pdf

From Tristar,  the TS-45 is good to 4KW, Now would I run that much through it? probably not, but my point is when saying something is only good to so much of a spec then you need to offer up the goods on that spec.

I am not sure what you are confused about.  The systems are different.  

PWM Pulse Width Modulation has an 80% charging efficiency due to its design.

MPPT Maximum Power Point Tracking is a more advanced system and has a 92% + efficiency.

If you are running a low power low budget system, the PWM is a decent choice.  If on the other hand you are running a higher power system, go with the MPPT.  It will pay for itself in power in quickly.  

Morningstar is a top brand, and also top dollar.  It can handle more power, but still it has the system design limitations.

 

[Canine]

Okay,I think I can accept the 12% gain you posted.I'll still have to say that I'm still skeptical of the 30% gain in amps with mppt.

 

[FALCON]

Bob - the MPPT charge controller is basically functioning like a transofrmer. It's converting power from one voltage to a different voltage. There's no magic increase in power. It's just changing the way the power is delivered.

Coming from the solar panel to the CC, each panel making 5.29 amps at 18.9 volts.

So Power = (Volts)*(Amps) = (18.9v) * (5.29amps) = 100 watts

When you wire four of those panels in parallel, you get (4)*(5.29) amps at the same voltage. So that's 26.45 amps.

So, power of 4 panels in parallel = (18.9v)*(21.16ams) = 400 watts

If I had wired those in series instead, I'd have this:
Power = (75.6v)*(5.29amps) = 400 watts.

See what's happening there? You're getting the same power, but it's coming in a different way. The amount of power delivered (or energy transfered) depends on both the Voltage and the Amps. One amp at 6v is half as much energy being transferred as one amp at 12v.

An MPPT charge controller functions sort of like a transformer. Power may be delivered on wires at 240volts (or 480 or whatever, I don't know). Then a transformer steps that down to 240 volts. The power being delivered doesn't just get cut in half and magically disappear (actually, you'd have a fire or something if half the power was being lost somehow), it gets converted into more amps.

So the MPPT takes that voltage of 18.9, and converts it down to 14.5 (or however much is needed). That's a change by a ratio of 14,5/18.9 - a reduction of 77%. If the transformation was 100% efficient, the amps would increase by the inverse of that, or 18.9/14.5 - which is a 30% increase. That's where the 30% you're doubting comes from. It's not a magic increase in amps. It's just an adjustment in the way that the power coming from the panels is delivered to the battery.

So going in to the CC you have:
Power = (18.9v)*(21.16amps) = 400 watts

and, if it were 100% efficient, after it converts the voltage to 14.5, you get:
Power = 400wats = (14.5v)*(??amps).

Using algebra, you get:
(??Amps) = (400watts)/(14.5v) = 27.58 amps.


Again - it's the same power, it's just being delivered differently. It's sort of like if you had a water system where:

Coming in to the converter, you have a big pipe, it's area (cross section of the inside of the pipe) is 1 square foot. The water is flowing at 100 cubic feet per minute.

The converter is just a transformation from that big pipe size to a smaller size. Say it's half the size = with an area of 0.5 square feet. The water doesn't disappear at the transform point - instead, it speeds up. So after the taper down, you have the 0.5 square feet pipe, and you still have 100 cubic feet of water per minute. So now the water must be flowing through the smaller pipe at 200cubic feet per minute. (This example is also similar in that, when the water goes through that taper section, there would be more turbulence than in the normal straight sections, which would cause more pressure loss than in the straight sections, meaning that the water flow gets reduced a little bit overall, maybe to 95 cubic feet per minute. I believe the "transformer" function in the MPPT would have some inefficiency also. But if I understand correctly, the MPPT has a higher overall efficiency than a PWM because of it's power point tracking ability. If that's the case, then the efficiency loss on the PWM would be more than on the MPPT and the MPPT would come out even farther ahead in the amps to battery calculations.

 

[FALCON]

in the water example above, here is how it compares to electricity flowing through a wire/system:

- The speed of the water flow (in linear feet per minute) is like the amps.
- The pressure that the water is being pushed into the pipe is like the voltage
- The flow of the water (in gallons per minute or cubic feet per minute) is like the power

You can change the pressure in part of the piping (by changing the pipe size) and make the water flow faster or slower. But it's still the same amount of gallons or cubic feet flowing through the system.

(if you don't get this example, think of what happens when you hold your thumb over the end of a garden hose. It makes the water shoot out way faster. It's basically the same amount of water coming out, but your finger is reducing the area that the water can flow through, so the speed of the water increases. The MPPT is basically acting like a thumb over the hose end - say, if you had to fill some container that had a small hole - that was smaller than the end of the hose itself. If you just position the hose towards the hole, only some of the water coming out of the hose would go through that hole. But if you put your thumb over the end and reduce the water stream size to match the hole size, now all the water from the hose can go through that hole)

 

[GotSmart]

I am not sure what you are confused about.  The systems are different.  

PWM Pulse Width Modulation has an 80% charging efficiency due to its design.

MPPT Maximum Power Point Tracking is a more advanced system and has a 92% + efficiency.

If you are running a low power low budget system, the PWM is a decent choice.  If on the other hand you are running a higher power system, go with the MPPT.  It will pay for itself in power in quickly.  

Morningstar is a top brand, and also top dollar.  It can handle more power, but still it has the system design limitations.

 

[GotSmart]

in the water example above, here is how it compares to electricity flowing through a wire/system:

- The speed of the water flow (in linear feet per minute) is like the amps.
- The pressure that the water is being pushed into the pipe is like the voltage
- The flow of the water (in gallons per minute or cubic feet per minute) is like the power

You can change the pressure in part of the piping (by changing the pipe size) and make the water flow faster or slower. But it's still the same amount of gallons or cubic feet flowing through the system.

(if you don't get this example, think of what happens when you hold your thumb over the end of a garden hose. It makes the water shoot out way faster. It's basically the same amount of water coming out, but your finger is reducing the area that the water can flow through, so the speed of the water increases. The MPPT is basically acting like a thumb over the hose end - say, if you had to fill some container that had a small hole - that was smaller than the end of the hose itself. If you just position the hose towards the hole, only some of the water coming out of the hose would go through that hole. But if you put your thumb over the end and reduce the water stream size to match the hole size, now all the water from the hose can go through that hole)

No, the analogy is not right.

PWM is a system that loses 20% of the power due to heat loss for the lack of a better term.  Electricity is a pulse, and the PWM  Modifies the pulse.  (Pulse Wave Modification)  It uses most of it but with primitive technology that cuts off a part of the pulse and loses it. 

MPPT has the capability of capturing more of the pulse.  (MAXIMUM Power Point Transfer)  It has more electronic components that are able to transfer the wave into a smaller unit. 92%

Putting the thumb over the hose is like kinking the hose.  You slow down the flow.  Not valid in this comparison.  The water is still there, but slowed down.  

With electricity the power coming in is transferred into heat and goes away.  Gone, not there for use.

 

[akrvbob]

Falcon, I apologize but I don't know what your point is, it got lost on me.  

The amps coming out of a solar panel can't be increased and a PWM controller isn't smart enough to increase it. When it steps down the volts to match the battery, those volts, watts and amps are simply gone, totally wasted and never put into your battery.

On the other hand, a MPPT is designed to step down the voltage and increase the amperage. It will give you 25-35% more amps into the battery over a PWM.

Here is an explanation from the Northern Arizona wind and Sun page. Maybe it will make it clearer for you.  http://www.solar-electric.com/solar-charge-controller-basics.html/

What happens when you use a standard controller

Standard (that is, all but the MPPT types), will often work with high voltage panels if the maximum input voltage of the charge controller is not exceeded. However, you will lose a lot of power - from 20 to 60% of what your panel is rated at. Charge controls take the output of the panels and feed current to the battery until the battery is fully charged, usually around 13.6 to 14.4 volts. A panel can only put out so many amps, so while the voltage is reduced from say, 33 volts to 13.6 volts, the amps from the panel cannot go higher than the rated amps - so with a 175 watt panel rated at 23 volts/7.6 amps, you will only get 7.6 amps @ 12 volts or so into the battery. Ohms Law tells us that watts is volts x amps, so your 175 watt panel will only put about 90 watts into the battery.

Using an MPPT controller with high voltage panels

The only way to get full power out of high voltage grid tie solar panels is to use an MPPT controller. See the link above for detailed into on MPPT charge controls. Since most MPPT controls can take up to 150 volts DC (some can go higher, up to 600 VDC) on the solar panel input side, you can often series two or more of the high voltage panels to reduce wire losses, or to use smaller wire. For example, with the 175 watt panel mentioned above, 2 of them in series would give you 66 volts at 7.6 amps into the MPPT controller, but the controller would convert that down to about 29 amps at 12 volts.

If you disagree, give me two sentences explaining exactly how you don't agree, then give me your reason.
Bob

 

[FALCON]

We're saying the same thing..

I'm not saying that the amps at the panels themselves are increasing.

 

[akrvbob]

Falcon, I'm glad to hear that. This is something i see all the time on the forum, two people will be saying the same thing but in different enough ways it seems like they disagree. Oddly, those cases usually end up with the most anger.

That's why I introduced a third party so we could both agree on their language.
Bob

 

[Canine]

Bob,you might be right if someone was using 33 volt panels.However in the real world most off grid applications are with 12 volt panels.I think I've beat this dead horse enough.

 

[FALCON]

No, the analogy is not right.

Putting the thumb over the hose is like kinking the hose.  You slow down the flow.  Not valid in this comparison.  The water is still there, but slowed down.  

With electricity the power coming in is transferred into heat and goes away.  Gone, not there for use.

The analogy is right. The water is absolutely not slowed down. It speeds up.

I'm guessing by "slowed down" you may mean the volumetric flow is decreased...? If that's the case, yes, the total volumetric flow will decrease some. This is because you're introducing more inefficiency and that drops the pressure some compared to what it would be without that inefficiency. And the MPPT has some inefficiency (8%?). I'm not talking about covering 95% of the end of the hose - Just like, i assume, you wouldn't have an MPPT or transformer converting all the way down to 0.1 volts and expect thousands of amps.

If you don't believe the hose thing, you can test it out yourself. Get a hose with a consistent water source, a bucket, and a stopwatch. Record how much time it takes to fill the bucket normally. Then record how long it takes to fill the bucket when you have your thumb covering half of the end of the hose (not more than that). It won't be all that different.